Regeneration of fischer-tropsch catalyst



Jan. 15, 1952 H? MARTIN ETAL 2,582,713

REGENERATION OF' F ISCI-.IER-TROPSCH CATALYST Filed Nev. 2a, 1947 SY MTHE@ 5 QaAdTow., 2O

SYnlTHas l l C 'EgNVEYEl- @amaai IU'an mag Patented Jan. 15,v 1952 REGENERATIN F FISCHER-TROPSCH ACATALYST Horner Z. Martinrlltoselle, and Ivan Mayer, Summit. N. J

gjno'rs 'to Standard Oil Developn'oent Comparti. a oorooration of Delaware .npplibationinovember 2s, iofiieeeriai .Navettes 'io claims. l(ci, 252-418,)

This invention relates to the catalytic :,conve r sion of carbon `oxides with hydrogen vto form valuable synthetic products. ,The invention is more particularly concerned with an 'improved method of employing and reconditioning ,finely divided catalysts having a high activity and selectivity for the formation `of normally liquid hydrocarbons in the catalytic conversion of .carbon monoxide with hydrogen .employing the so-.called uid solids technique.

The synthetic production vof liquid hydrocarbons from gas mixtures containing various proportions of carbon monoxide and hydrogen lis already known and numerous catalysts, usually containingv an iron group metal), have .been described which are specifically active in promoting the desired reactions at certain preferred operating conditions. For example, cobalt .supported on an inert carrier is used when .relatively `low pressures (atmospheric to about 5 atmospheres) and low temperatures (about 37 5"?425 F.) are applied in the manufacture of a substantially saturated hydrocarbon product while at ,the higher temperatures v(about 450750 F.) .and higher pressures (about A5-,25 atmospheres and higher) required for the production Yof lll'isatn-` rated and branched-chain products of high antiknock Value, 'iron-type catalysts are lmore ,stuitable;

In both cases, vthe reaction is ,stronglyexothermic and the utility of the catalyst declinessteadily in the course of the reaction, partly .due `to the deposition of non-volatile conversion .prodeucts such as carbon, parain wax, and thelike, on the catalyst.

r'he extremely exothermic lcharac ter ,and high temperaturel sensitivity of the synthesis reaction and the relatively rapid catalyst deactivation have led, in recent years, Atothe application of the so-called nuid solids technique .wherein the syn.- thesis gas is contacted with a yturbulent bed {Off finely divided catalyst fluidized bythe gaseous 'reactants and products. This technique permits continuous catalyst replacement and jgreatlyirn! proved heat dissipation and temperature control.

However, the vadaptation Vof `the r1hydrocarbon synthesis to the fluid solids technique hais encountered serious difliculties', 4particularly with respect to catalyst deposits and their detrimental effects on the fluidization characteristics and 4.thesizing .activity and selectivity toward normally rliquid products with a strong tendency to lcarbonize during the synthesis reaction, that is, lto form `xed carbon 'or coke-like catalyst deposits yvhich can not be readily removed'by con- `ventional methods of synthesis catalyst regeneration such aSeXtraction, or the like.

,Ihese carbon deposits, when allowed to accumulate, weaken the catalyst structure and lead to rapid catalyst disintegration. The reduction ,of the true density of vthe catalyst resulting from its high content of low-density carbonv coupled with therapid disintegration of the catalyst particles causes the vfiuidized catalyst bed to expand, thereby reducing its concentration of catalyst and ultimately resulting in the loss of the catalyst bed .because it `becomes impossible to hold 'the catalyst in a dense phase at otherwise similar nuidization conditions. With these changes in iluid bed characteristics, the heat transfer from and throughout the bed decreases markedly, fayoring further carbonization and accelerating the deterioration of the uidity character- ,ittica o f the ,bod-

These difficulties .may be overcome, quite generally, by subjecting the carbonized catalyst conltlllO'llSly Or intermittently to a regenerating treatment 'by which carbon is burnt on the catalyst with the aid of an oxidizing gas. However, oxidative regeneration of the catalyst, if not `:carefully controlled with respect to the oxidation conditions, lmay frequently lead to an undesirable over-oxidation of the iron component of the catalyst. VIn addition, such catalyst nes of lun- Ldesirablysmall particle size as have been formed prior Vto regeneration are not restored to the original rreadily fluidzable particle vsize by this regeneration treatment, particularly when carried Ioutvin fluid type regenerators. These lines may, therefore, continue to accumulate and eventually interfere with an eflicient operation fofthe process unless they are discarded from the 'catalyst cycle, which, of course, constitutes an appreciable loss of valuable material.

'The present linvention overcomes these diniculties `and affords various additional advantages 'fas will appear from the following description l'wherein reference will be made to the accompanying drawing.

In accordance with the present invention, catalyst carbonized and disintegrated in the catalytic synthesis of hydrocarbons fromCO and is continuously or intermittently subjected to via combined oxidation and sintering treatment v-tvitlo-xat `free-m'rygen vcontaining gas "such as air at temperatures of about 14002000 F. followed stantial proportions of alkali metal promoters may be lost, the cool catalyst is preferably ima preferred embodiment of the invention, two rotary kilns are used in the first of which the catalyst is sintered and oxidized with countercurrently owing air, while in the second kiln the catalyst is subjected to reduction with a concurrently flowing reducing gas mixture of the Having set forth its objects and general nature,

vthe invention will be best understood from the `.more detailed description hereinafter in which "reference will be made to the accompanying A, drawing, the` single figure of which is a semipregnated with a suitable solution of a promoter such as the halides, carbonates or hydroxides of sodium or potassium, prior to its return 5to the synthesis stage. A v

For the purpose of reduction, the relatively diagrammatic illustration of a system suitable for carrying out a preferred embodiment of the invention.

. j; Referring now tothe drawing, the system illus- 'tratedmtherein ressentially comprises a synthesis expensive hydrogen normally usedas a reducing agent is replaced by a reducing atmosphere formed on the catalyst undergoing `reduction',"` by contacting the oxidized and sintered catalyst with carbonaceousr materials Vand air ,and/or steam at temperatures suitable for thereduction of the oxidized catalyst. Coke, coals, lfuel Voils and fuel gases including methane may be used as Vcarbonaceous materials. In accordance with a preferred embodiment of the invention, suicient carbon Vis left on the catalyst during the sintering treatment to react with steam and/or air admitted tothe reducing zone so as to forma suitable reducing mixture, if necessary in cooperation with extraneous solid, liquid or gaseous fuel admitted to the reduction zone. Complete reduction to metal of the catalyst oxidized during the sintering treatment is frequently not required.

It has been found that at relatively high temperatures of about 1200" to 2000 F. it is possible to produce, by the reaction of steam with coke or other carbonaceous fuels, 'a gaseous mixture of hydrogen, water vapor, carbon monoxide and carbon dioxide which will be oxidizing Vwith respect to carbon but will tend to 'reduce iron oxide to metallic iron. For this purpose, the feed ratio of steam to carbonaceous fuel should be so controlled that the values of the volumetric ratio CO2 CO and the Vsum of the partial pressures P'co-tPco2 stay below those giveni'nY the table below for various temperatures.

Temperature, F 1100 1200 1300 1472 PCo-l-Pcm, atm 0. 132 0. 42 .1. 32. 6. 14 Pcoz/Pco 0. 84 0. 74 0. 65 0. 52 Minimum Pcoz/Pc 50 0. 44 36 1 30 Oxide type FeO FeO FeO FeO This mode of operation is described and claimed specifically in the copending Martin, Mayer and l Tyson application, Serial No. 788,538, le'd of even date herewith and assigned to the same interests, which is here expressly referredto."

Operation in two subsequent sintering and reduction stages affordsl the advantage of I high process exibility. However, it is noted that satisfactory results may often be secured by treating the catalyst in a single stage .at conditions conducive to decarbonization and sintering and simultaneous reduction of iron oxideby .reactor I0,.a.sintering reactor 30 and a reduction reactor 40, whose functions and cooperation will be forthwith explained.

In operation, synthesis reactor IIl contains a "dense, turbulent, fluidized mass of iron catalyst Vsuch as sintered pyrites ash promoted lwith about 1.5% of potassium carbonate and having an original particle size of about 20-100 microns, preferably 50-100 microns.V Synthesis feed gas ccntaining about 0.83.0 volumes of H2 per volume of CO is supplied from line I to reactor I0 at a suitable synthesis pressure of 5-50 atm., preferably 20-40 atm. The synthesis temperature may be maintained between the approximate limits of 500 -800 F., preferably between about 550 and 700 F., by conventional methods of heat removal (not shown). Details of the operation of fluid synthesis reactors using iron catalysts are well known and need not be further specified here.

As stated before, carbon is deposited on the catalyst in reactor I0 and in about 100 hours as much as 50 lbs. of carbon may be deposited on each lbs. of catalyst. This will tend to diminish the activity of the catalyst and also cause its physical disintegration so that fines having particle sizes smaller than 20 microns will be formed in excessive quantities. If this condition is not corrected, the density of the catalyst phase will drop rapidly and the entire catalyst will be eventually blown out of reactor I0. ,The present invention corrects this difficulty by subjecting the carbonized and partially disintegrated catalyst to an oxidative sintering treatment in reactor 30 followed by a reducing treatment in reactor 40 and by regrinding to the desired size as will appear more clearly hereinafter.

By way of example, it is assumed that 100 lbs. per hour of catalyst expressed as pure iron, containing about 15.5%`coke on iron, 6.0% O2 on iron, and about 40% of fines smaller than 20 microns particle size, is to be decarbonized and "restored to, its original particle size. The car'- bonized and partially "disintegrated catalyst is withdrawn downwardly through a system of lockhoppers I2 Vwherein thepressure may be reduced to atmospheric at which the catalyst may be treated in reactors 30 and 40.

After pressure release, thecatalyst is con va readily owing state by admitting through line I8 an aerating gas, suchas air, flue gas, steam, etc. .which vmay be withdrawn through Yline 20. From hopper I6 the catalyst is fed by .gravity via .feeding means 2'5 to the upper end of reactor 30.

which may have the form of a conventional rotary kiln. Simultaneously, airis blown from line 32 into the lower end of reactor '30. Theamount of air admitted should be sufficient to heat the catalyst by combustion of coke Ato a temperature high enough to 'cause sinterling of the catalyst and the formation of larger catalyst agglomerates from the fines present. Reaction temperatures of about l2002000 F. are suitable `for this purpose. Thus, reactor 30 may be 'so operated that an average temperature of about l900 Ell-.fis main'- tained while about 90% of 'the carbon burned off and about -to 35% by weight of yoxygen is bound by the iron. Anamount of about 5,000 to 9,000 standard cu'.` ft. of air per hour is suitable to establish these conditions in thE 'case 'of the specic example here involved. If desi-red, heat may be removed from vreactor 30 in any'conventional manner, such as use of excess air., recirculation ofc'ooled solids, injection oa waterspray, etc. Spent oxidizing gas ls removed through line 33, preferably after a suitable gas-solids separation in conventional equipment such as acyclone separator (not shown) from which separated sol ids may be returned to reactor 30.

The sintered and oxidized catalyst is supplied.

at the outlet temperature of reactor 30, i. e. about l5001900 from the lower end of reactor to a feeding and mixing means 34 wherein it is mixed with subdivided coke or a similar carbonaceous fuel supplied from line 35. The mixture of sintered catalyst and fuel enters the upper end of reactor which may likewise be a rotary kiln of suitable dimensions. Simultaneously with the solids feed, a mixture of steam and air is supplied to the upper end of `reactor 40 from lines 38 and `39, respectively. The relative amounts of fuel, air and v'steam are vso controlled that an atmosphere reducing with respect to iron oxide is for-med within reactor '40 bythe conversion of the -fuel with "steam into vCO 'and H2 while, at the same time, suiilcient heat is generated by the combustion of fuel with air tosupvport the endother-mic Water gas and reduction reactions. At the conditions ofthe present examu ple, this may be accomplished byrfeedi'ng about l5 to 25 lbs. of coke, 1,000 to ,1,300's`tandard cu. ft. of air and 2 to l0 lbs. of steam. These 'proportions are based on a preheat of the Yair-"stear'n mixture of about .500-1500 F. Tin heat exchange with flue gases from reactor 130 4and/or 40.

It will be appreciated that 'the gas at the vinlet of reactor 40 is oxidizing with respect to Aboth iron and coke, since -it consists mainly of air vand steam. However, -i-n the -lower portions of reactor 40 the air, steam and coke will have had opportunity to react and, therefore, gases reducing with respect to iron will be obtained. The temperature of the solids entering reactor 40 will be in the neighborhood of 1500 to 1900 F. at which the catalyst was removed from reactor 30. The temperature of the outlet gas and solids depends on the fuel, air and steam quantities and preheat.

In any case, the steam, air and coke rates may be so controlled that the desired gas composition is obtained prior to the discharge of the catalyst from reactor 40. Thus, it may be stated, quite generally, that for a discharge temperature of about 1500 F. these rates should be so controlled that the ratio of CO2 to CO is less than about 0.5. At 1800 F. this ratio should be less than about 0.4. These conditions may be easily met by varying the quantity of steam charged to the kiln, no matter whether reactor 40 is heated externally or, as described above, operated substantially adiabatically by the admission of controlled amounts .of air. The treatment of 'the catalyst with a CO-i-Hz mixture rather than Vpure H2 has, at relatively low temperatures within the ranges indicated above, the further advantage of suitably preconditioning the catalyst for lthe subsequent synthesis reaction, since it has been found that the carbonization tendency of iron catalysts maybe substantially reducedby apretreatment with C0 at elevated temperatures conducive to carbide formation.

The sintered, deearbonized 'and reduced catalyst discharges from the lower end of reactor 40 into,I a quenching chamber 42 wherein the temperature ofthe catalyst may bereduced to yabout 10W-500 F., lby heat exchange with catalyst cooled by quench water in vessel 43 and recirculat'ed tochamber :l2 through line d'5 4by any :com ventional means. Chamber "l2 may vhave the function of, or comprise a conventional gassolid-s separator, such vas a cyclone. Quench Water may be introduced through line 44. The catalyst cooled to about 200 F. passes, by gravity. into va conventional grinding and sizing device te from which it discharges at a particle size of about -100 microns into lockhopper system 48.`

Device te vmay comprise sieving and/or elutriation means suitable for properly sizing the ground catalyst. Particles of undesirably .small size may be discarded through line 50 or returned to reactor 30 for resintering. l

As a result of the high temperatures employed in reactors 3e and 40, substantial proportions of the alkali metal promoter content of the catalyst may be lost. This promoter may be advantageously replaced at any point of the system after it leaves quenching zone 42. For example, a suitable promoter solution, such as an aqueous solution of a potassiumhydroxide, carbonate or halide, may be injected throughline 5l into the catalyst leaving grinding device 46. Addition of the promoter at this or asimilar point rather than in the synthesis reactor is of advantage since the catalyst at this point is free of oil and coke and the promoter may thus4 pep- Strate the catalyst much more effectively than if Aitis added to the catalyst in the synthesis reactor.

Properly sized regenerated and reduced catalyst may be passed fromlockhoppers 48 at the synthesis pressure to synthesis gas feed line l to be returned therein as a dilute suspension of solids-in-gas lto synthesis reactor l0 for reuse. The system illustrated by the drawing vpermits of various modications. Reactors 30 and/or'40 may be operated at elevated pressures, if desired, so that pressure reduction on the catalyst may be substantially minimized. Either one or both lockhopper systems i2 and 48 may be replaced by standpipes or mechanical conveyors, if the pressure conditions permit. Concurrent rather than countercurrent now of gases and solids may l be applied to reactor 30.

As previously indicated, decarbonization, sintering and reduction may also be carried out in a single reactor oi the type of reactors 30 and 40, by properly controlling the reaction temperature in combination with the composition of the regenerating atmosphere. For example, this may y be accomplished by feeding spent catalyst, air,

1. The process of maintaining a fluidizable particle size distribution and a low carbon concentration in a dense, turbulent, iluidized bed of finely divided carbonizing catalyst used in the synthesis of' hydrocarbons from carbon monoxide and hydrogen, which comprises withdrawing carbonized catalyst containing nes having a particle size below the iluidizable range from said bed, subjecting said withdrawn catalyst in a sintering zone to an oxidizing Vsintering treatment adapted to remove carbon from the catalyst and simultaneously agglomerate catalyst fines to larger aggregates, subjecting the oxidized and sintered catalyst in a reducing zone to a reducing treatment in the absence 'of extraneous hydrogen with a reducing gas generated in said reducing zone by a reaction of steam and air with a carbonaceous fuel, controlling the temperature in said reducing zone by controlling the amounts of air and steam introduced thereto, grinding the reduced catalyst to a fluidizable particle size, and returning ground catalyst to said bed.

2. The process of claim 1 wherein the catalyst is subjected to a tumbling motion in at least one of said zones.

3. The process of claim 1 in which said sintering and reducing treatments are carried out at a temperature of about 14002000 F.

4. The process of claim 1 wherein a portion of tion in a dense, turbulent, iluidized bed of iinely divided carbonizing iron-type catalyst used in the synthesis of hydrocarbons from carbon monoxide and hydrogen, which comprises withdrawing carbonized catalyst containing nes having a particle size below the uidizable range from said bed, subjecting said withdrawn catalyst to a high flu temperature treatment with oxidizing gases in thev absence of extraneous hydrogen,y said treatment being adapted to remove carbon from said catalyst, to sinter said catalyst so as to form larger aggregates from said catalyst fines, and to reduceiron oxide to iron, grinding said heattreated catalyst toa uidizable particle size and returning ground catalyst to said bed.

7. The process of claim 6 wherein said heat treatment is carried out in a single zone to which air, steam and carbonaceous fuel are supplied in proportions adequate to` maintain a sintering temperature and an atmosphere oxidizing to carbon but reducing to ironvoxide.

8. The process of claim 7 in which said catalyst subsequent to being subjected to said reducing treatment is cooled by heat exchange with quenched reduced catalyst and thereafter quenched in water.

9. The process of claim 7 wherein said fuel is comprised of the carbonaceous deposit formed on said catalyst during the hydrocarbon synthesis reaction.

10. The process of claim 7 in which said sintering and reduction treatment is carried -out at a temperature of about 1400 to 2000 F.

HOMER Z. MARTIN. IVAN MAYER.

REFERENCES CITED The following references are of record in the 'lle of this patent:

UNITED STATES PATENTS Number Name Date 133,202 Chubb Nov. 19, 1872 1,562,550 Hall Nov. 24, 1925 1,598,967 Hiller Sept. 7, 1926 1,915,362 Hanks et al June 27, 1933 2,183,146 Michael Dec. 12, 1939 2,234,246 Groombridge Mar. 11, 1941 2,254,806 Michael Sept. 2, 1941 2,337,684 Scheineman Dec. 28, 1943 2,358,039 Thomas et al Sept. 12, 1944 2,360,787 Murphree et al Oct. 17, 1944 2,393,909 Johnson Jan. 29, 1946 2,417,164 Huber, Jr Mar. 11, 1947 2,420,049 Martin May 6, 1947 2,438,584 Stewart Mar. 30, 1948 2,455,419 Johnson Dec. 7, 1948 2,462,861 Gunness Mar. 1, 1949 2,467,803 Herbst Apr. 19, 1949 2,479,420 Segura Aug. 16, 1949 2,483,850 Segura et al. Oct. 4, 1949 2,510,823 Krebs June 6, 1950 

1. THE PROCESS OF MAINTAINING A FLUIDIZABLE PARTICLE SIZE DISTRIBUTION AND A LOW CARBON CONCENTRATION IN A DENSE, TURBULENT, FLUIDIZED BED OF FINELY DIVIDED CARBONIZING CATALYST USED IN THE SYNTHESIS OF HYDROCARBONS FROM CARBON MONOXIDE AND HYDROGEN, WHICH COMPRISES WITHDRAWING CARBONIZED CATALYST, CONTAINING FINES HAVING A PARTICLE SIZE BELOW THE FLUIDIZABLE RANGE FROM SAID BED, SUBJECTING SAID WITHDRAWN CATALYST IN A SINTERING ZONE TO AN OXIDIZING SINTERING TREATMENT ADAPTED TO REMOVE CARBON FROM THE CATALYST AND SIMUL- 